1. Field of the Invention
The present invention relates to computer networks. More particularly, the present invention relates to a resource reservation system in a computer network to support end-to-end Quality-of-Service constraints.
2. Description of the Prior Art
Quality-of-Service (QOS) typically refers to a predetermined minimum latency and minimum data transfer rate supported by a computer network. Point-to-Point QOS is typically implemented within prior art networks by reserving resources through a path from the source node to the destination node (see the Resource Reservation Protocol or RSVP an overview for which is provided in the text book Managing Bandwidth—Deploying QOS in Enterprise Networks, by Alistair Croll and Eric Packman, Prentice Hall, Upper Saddle River, N.J., 1999; and “Resource Reservation Protocol (RSVP)—Version 1 Functional Specification”, Braden, R., Zhang, L., Berson, S., Herzog, S., Jamin, S., RFC 2205, September 1997, Proposed Standard). Reserving resources throughout the transmission path guarantees that the connection will support a desired QOS for a specified period. Implementing QOS constraints requires knowledge of the resources in each node and the connection between the nodes in the network including the transmission latencies and bandwidth.
Consider, for example, the prior art computer network 2 shown in FIG. 1. When client computer 4B attempts to access a data stream stored on a disk drive 6 attached to network server 8, a transmission path 10 through nodes 16a and 16b may be established by reserving the necessary resources at each node to support predetermined QOS constraints such as latency and data rate. During the life of the reserved transmission path 10, nodes 16a and 16b may be inaccessible by other client computers (e.g., client computer 4C) if either node lacks the resources to handle additional traffic.
Because the mechanical latency of the disk drive 6 is not taken into account in the QOS equation, the network server 8 will typically buffer a sufficient amount of the data stream so that the mechanical latency of the disk drive 6 does not impact the QOS constraints. However, this implementation may require a significant amount of buffer memory and processing power at the network server 8 in order to support multiple, simultaneous streams. Further, for certain business transactions, such as bidding on auctions over a network, the QOS constraints could be on the order of milliseconds. In such applications it may become impractical or even impossible to satisfy the QOS constraints due to the mechanical latencies of the disk drives responsible for servicing the transaction data.
There is, therefore, a need to reduce the complexity and cost of implementing QOS constraints in a computer network, particularly with respect to the mechanical latencies of disk storage devices. In particular, there is a need to support QOS constraints on the order of milliseconds in transactions executed over a computer network.